Surface structure of stimuli-responsive polystyrene particles prepared by dispersion polymerization with a polystyrene/poly(l-lysine) block copolymer as a stabilizer

A block copolymer composed of polystyrene and poly(α-l-lysine hydrobromide) (PLL) segments was used as a stabilizer for dispersion polymerization of styrene in water–methanol medium to give narrowly-distributed polystyrene particles in the size range from 0.36 to 1.09 μm, on which the PLL segment was grafted with a surface density of 0.2–3.4 l-lysine residue/nm2. We investigated effects of polymerization time, stabilizer concentration, segmental composition of the block copolymer, and composition of the medium on surface structure and particle size of the affording particles. Interestingly, we obtained an experimental evidence that the surface density of the PLL clearly depends on structural parameters of the stabilizer and various polymerization conditions. Based on the dependence, it was possible to control the surface density of the narrowly-distributed particles within the range between the minimum and the maximum density limits of the graft chain by changing the structure of the stabilizer and polymerization conditions. Conformation of the PLL, which underwent a helix–coil transformation with an increase in water composition of the medium, had a strong effect on the surface structure, the size, and property of the resulting particles. Further modification of the particle surface was possible by utilizing the amino groups in the PLL graft.